1. Field of the Invention
The present invention relates to a rectifier for an alternating current generator for a vehicle and particularly relates to an arrangement of heat sink for supporting diodes of the rectifier.
2. Description of the Prior Art
FIG. 4 is sectional view showing a conventional alternating current generator for a vehicle and the alternating current generator consists of a case consisting of a front bracket 1 and a rear bracket 2 made of aluminum, a shaft 6 being disposed in the case 3 and having a pulley 4 being fixed at an end of the shaft 6, a rundle type rotor 7 secured to the shaft 6, fans 5 fixed at both side surfaces of the rotor 7, a stator 8 fixed to an inner wall within the case 3, slip rings 9 being fixed to another end of the shaft 6 and for supplying electricity to the rotor 7, a pair of brushes which slide on the slip rings 9, brush holders 11 for storing the brushes 10, a rectifier 12 being electrically connected to the stator 8 and for rectifying the alternating current generated through the stator to a direct current, a heat sink 17 fit to the brush holder 11, and a regulator being bonded to the heat sink 17 and for regulating the magnitude of the alternating current voltage generated through the stator.
The rotor 7 consists of a rotor coil 13 for producing a magnetic flux by supplying electric current therethrough and a pole core 14 being arranged to cover the coil 13 and for producing magnetic poles due to the magnetic flux passing through the core 14. The pole core consisting of mutually mated first core 21 and second core 22, and those cores 21 and 22 are made of iron and have claw shaped magnetic poles 23 and 24 respectively.
The stator 8 has a stator core 15 and stator coils 16 wound around the stator core 15. The stator 8 generates the alternating current through the stator coils 16 due to the variation of the magnetic flux from the rotor coil 13 produced as a result of rotation of the rotor 7.
As shown by FIG. 5, the rectifier 12 consists of heat sinks 25 for supporting a plurality of diodes 26 on the plus side and heat sinks 27 for supporting a plurality of diodes 28 on the minus side. The plus side heat sink 25 has fins 25a. The plus side heat sink 25 and fins 25a are formed to be a single body, and the minus side heat sink 27 shares function of earth and is directly connected to the rear bracket 2.
The heat sinks 25, 27 are formed to be horseshoe shaped from the material such as ADC10 and ADC12 by means of aluminum die-casting.
On account of space efficiency, those diodes 26 and 28 are secured by means such as soldering on the heat sinks 25, 27 with an optimum positioning securing a good thermal conduction.
Also another arrangement can be seen such that diodes are fixed and supported so that their longitudinal directions come out to be in parallel with respective axes of the heat sinks and the fins of the heat sinks of both sides of plus and minus are placed being perpendicular to that axes.
In the alterating current generator mentioned as above, the magnetix flux is produced by supplying electric current through the rotor coil 13 through the slip rings 9, and by this magnetic flux, the claw shaped magnetic pole 23 of the first core body 21 is magnetized to N pole and the claw shaped magnetic pole 24 of the second magnetic body is magnetized to S pole.
On the other hand, because the pulley 4 is driven by the engine and the rotor 7 is rotated by the shaft 6, a rotating magnetic filed is applied to the stator coil 16 resulting in a generation of an electromagnetic force corresponding to the variation of the magnetic field. This electromotive force is rectified by the rectifier 12 to a direct current and its magnitude is regulated by the regulator 18 and the electricity is charged to unshown battery.
The cooling air stream produced by the fan 5 rotated by the shaft 6 are taken into the interior of the case 3 from the air intake port 1a, 2a of the front bracket 1 and the rear bracket 2, respectively and on the rear side the air stream passes through heat generating members such as the rectifier 12 and regulator 18 and cools those heat generating members and also passes through the fan 5 from its inner radius side to its outer radius side and cools front end and rear end of the stator coil 16 and is exhausted from the exhaust port 1b and 2b of the front bracket 1 and the rear bracket 2, respectively.
Heat sinks 25 and 17 of the rectifier 12 and the regulator 18 those of which have high degree of heat generation and affect output performance due to high temperature, in order to promote heat dissipation, are provided with fins 25a and 17a, respectively and are adapted to introduce cooling air stream thereinto.
Among the heat sinks of the rectifier 12, the minus side heat sink 27 has no fins but the air intake port 2a on the side of grownded rear bracket 2 serves as fins of heat sink 27 mentioned as above, and thus the same cooling is performed.
Now in the conventional rectifier as mentioned above, in order to improve thermal conductivity, productivity and reliability, respective diodes were fixed to heat sinks by soldering after forming a metal coating layer (meshed portion in the drawings) having a good solderability such as Ni plating on to the surface of heat sink 27, 25 of aluminum die-cast as shown by FIGS. 6(a), (b). Though the portions to be coated which is actually necessary for soldering are limited merely to the recessed portion 25b, 27a for fixation of diodes, for consideration of reasons such as coating process the heat sink body being kept intact is diped into a coating solution bath and thus whole heat sinks 27, 25 are obliged to be coated.
On the other hand, because of generation of high calorific value by diodes 26, 28 due to a sustained continuous electric current during generations of electricity by the generator, as the number of diodes increases the cooling function is maintained by correspondingly enlarging the heat sinks for cooling. To perform heat dissipation correspondingly to the increased calorific value, total area of fins are arranged to be increased by diminishing pitch of the fins 25a and increasing the number of fins.
Accordingly, fin portion which is not required to be coated increases apace.
Thus as seen in the conventional heat sinks, when whole heat sinks 27, 25 are coated, the area, which must be coated but is not necessary to be served for soldering, is further increased and thus there gives rise to a problem of raising up the surface treatment cost rapidly.